As computer-based systems, such as game consoles, appliances, personal computers (“PCs”), servers, personal digital assistants (“PDAs”), cellular phones, automated teller machines (ATM), have become more prevalent in recent years, the portability of systems as well as human-machine interface devices becomes increasingly important. Currently available user interface devices, such as keyboards, computer mice, joysticks, phone pads, remote controls, and/or touch screens, have various physical limitations and constraints. For example, a problem associated with the conventional user interface devices is portability because they are typically large and awkward to carry. Another problem associated with typical conventional user interface devices is lack of ergonomic considerations because various physical motions associated with button presses and key strokes can increase user's physical fatigue and discomfort.